1. Field of the Invention
This invention relates generally to a rotary filter apparatus, and more particularly to a new and improved backflushable, rotary filter apparatus primarily intended for use in filtering high viscosity polymer hot melt feed stocks, which is capable of backflushing the filter surface areas to purge contaminants from the apparatus without interrupting the filtering operation. The filter apparatus of this invention provides a continuous, uninterrupted flow of the hot melt through a plurality of filter elements mounted within a rotatable housing such that the flow of hot melt is smooth, unrestricted and devoid of "dead spaces" where there could be "zero flow" thereby virtually eliminating thermal degradation of the hot melt. The filter housing can be periodically rotated to successively and automatically pass one filter element at a time through a backflush position to thereby automatically and sequentially backflush each filter element to purge filtered contaminates from the apparatus without removing the other filter elements from service or otherwise interrupting the filtering operation, and without the need for any valves to control the backflush operation.
2. Summary of the Prior Art
There are a number of manufacturing processes involving the formation of products from molten polymer feed stocks, such as nylon, polyesters and other polymers, wherein it is highly desirable to operate on a continuous flow basis. Such processes typically embody extrusion, injection, blow molding, coating spraying techniques, etc., to manufacture a variety of products, such as synthetic textile fibers, plastic tubing, plastic sheets and films, protective coatings, insulation on electrical wire, and the like. Because of the difficulties in initially starting up such processes and cleaning the equipment after a shut down, it is highly desirable to operate such processes on a continuous, uninterrupted flow basis for as long a period of time as can be sustained.
In most of the processes noted above, it is the usual practice to include a filter unit in the "hot melt" flow stream to effect removal of particulate impurities and gel matter which otherwise could result in the production of defective products, or which could cause clogging of downstream equipment such as spinnerettes or extrusion dies. Naturally, such filters must be cleaned or replaced on a periodic basis. Rather than shutting down the process to clean or replace such filters, it is common practice to utilize a dual filter system to permit continued, uninterrupted operation. That is, the process hot melt is routed through only one of the dual filter systems at a time so that the filter system not in use can be cleaned or replaced, and put in stand-by condition so that it can be put into service when it is time to shut down the other filter system for cleaning or replacement. A diverter valve must be provided to switch the hot melt flow from one filter system to the other.
More recently, self-cleaning filter systems have been introduced which offer fully automatic filter cleaning or changing without the need for any dual filter system, without any notable production delays, and without any operator involvement. One such filter apparatus described in Melt Filtration Report, Issue 83-1, April-May, G. F. Goodman and Sons, Inc., Philadelphia, Pa., utilizes a cylindrical pack of filter screens disposed between a pair of perforated, annular housing cylinders sharing a common axis. In this apparatus, the unfiltered hot melt is passed into an inlet manifold encircling the outer cylinder which is provided with a plurality of inlet ports to feed the hot melt radially inward and through the annular pack of screens, and through a plurality of outlet ports through the inner cylinder which are aligned and registered with the inlet ports in the outer cylinder.
The self-cleaning feature of the apparatus is based on an automatic response to the outlet pressure of the hot melt so that when the pressure drop exceeds a preset limit, the outer cylinder is automatically caused to partially rotate to register an inlet port with an outlet channel whereby hot polymer within the inner cylinder will backflush that inlet port.
Another self-cleaning filter system has recently been introduced by Gneuss Kunststoffechnik GmbH, Oenhausen, Germany, which comprises a plurality of disk type filters disposed in a circular pattern on a disk wheel rotatably mounted between a front and rear end plate. Registered inlet and outlet ports are provided through the end plates so that the hot melt can be passed through one or two of the disk filters disposed between the registered inlet and outlet ports. As the disk filters become clogged, the disk wheel is periodically rotated through a small arc to expose a fresh, clean filter disk or portion thereof, between the inlet and outlet ports as a comparable filter area is rotated out from between the two ports. Each filter disk is eventually rotated to a position not between the two end plates so that a fouled or damaged disk can be removed for cleaning or replacement. In addition, some models rotate the filter disks to a backflush position which is between the two end plates. At this position, a backflush chamber is provided on the back side of a filter disk and a backflush outlet on the other side of the filter disk. A small by-pass port is provided from the outlet port through the back end plate to the backflush chamber to force backflushing hot melt through the filter disk at this position and purge contaminants therefrom. Since a filter disk will always be disposed between the backflush chamber and the backflush outlet port, a shut-off valve is provided on the backflush circuit to minimize the amount of hot melt utilized for backflushing purposes.